The problem this invention addresses is that people forget their smartphones, tablets or other mobile devices, and then they get stolen. This is particularly worrisome as smartphones are now enabled to process payments through apps such as Apple Pay and Android Pay.
Although there are tracking apps that track a person's mobile phone, thefts usually take place too quickly for tracking apps to be useful, because the owner of the mobile device may not notice that it has been stolen in time to successfully use the tracking ability to find the phone. Also, the thieves may disable tracking or take apart the device or shut off the device thus shutting down tracking or otherwise cause the tracking to not help locate the phone.
Some Bluetooth devices have ranges of up to 100 m, and so a Bluetooth device which sounds an alarm only when the Bluetooth signal is lost from a mobile device is really already too far from the owner's range of vision or control to be useful.